So-called “pollywog” craters on Mars are small (about 0.5 to 15 kilometers in diameter) that have a single outlet channel at the lowest point of their rim with no discernable inlet channel. (They somewhat resemble tadpoles in shape). These outlet channels are evidence that the craters were once filled with water and overspilled.

As there is no inlet channel, the water source must either have been groundwater infiltration, precipitation (rain or snow), or subglacial melt. Most pollywog craters are found in the mid-latitudes where melting of ice was possible during Mars’ past. However, this crater is more in the equatorial region, so the water source was more likely groundwater.

This HiRISE image shows an eroded deposit on the floor of a potential pollywog crater, with a lobe-shaped, scalloped margin and visible layers. This deposit is likely sedimentary in origin, with materials having been deposited over time at the bottom of the crater lake. This unique site would be ideal for future astrobiological investigations.

Written by: Dan Berman  (26 August 2026)


This is a stereo pair with ESP_092760_1830.